The present invention relates to a steering apparatus for a vehicle in which a steering mechanism for changing a direction of tire wheels is not mechanically connected to a steering wheel, a steering torque applied to the steering wheel is obtained and an electric motor included in the steering mechanism is driven and controlled in accordance with the calculated steering torque, thereby increasing or decreasing a steering angle.
A steering operation of a vehicle is performed by operating a steering device arranged within passengers"" room, for example, by transmitting a rotation of the steering wheel to the steering mechanism which is arranged outside the passengers"" room for directing tire wheels (generally front tire wheels).
In recent years, there has been widely spread a steering apparatus (a power steering apparatus) for vehicle structured such as to arrange an actuator for steering assistance such as a hydraulic cylinder, an electric motor or the like in the middle of the steering mechanism, drives the actuator based on a detected result of operating force applied to the steering wheel to assist an operation of the steering mechanism in accordance with the rotation of the steering wheel, thereby reducing labor and load of a driver for steering.
However, in the conventional steering apparatus mentioned above, a mechanical connection (linkage) between the steering wheel corresponding to the steering device and steering mechanism is required, so that there is a problem that an arranging position of the steering wheel within the passengers"" room is limited to a position at which the connection with the steering mechanism outside of the passengers"" room can be achieved, and further, even in the case that the steering wheel is arranged at connectable position, a complex connecting structure is required for realizing the connection, so that this becomes a reason of interrupting the vehicle from being reduced in weight and its assembling process from being simplified.
For example, in Japanese Utility Model Publication No. 2-29017, there is disclosed a steering apparatus such as a linkless (drive-by-wire) power steering apparatus which is aimed to solve the problem mentioned above. In this steering apparatus, the steering wheel is mechanically separated from the steering mechanism and an electric motor such as an actuator for steering is arranged in the middle of the steering mechanism in the same manner as that of the actuator for steering assistance in the conventional steering apparatus. The structure is made such that the steering operation is performed in accordance with the operation of the steering wheel by driving the electric motor based on a detected result of operating direction and operating amount of the steering wheel.
The linkless steering apparatus structured in the manner mentioned above has advantages for automobile technology development future such as realizing a new steering device such as a lever (a joy stick), a pedal in place of the steering wheel, realizing an autopilot system in accordance with a route information obtained by detecting guide signs on a road surface and by receiving a satellite information, in addition to the scopes mentioned above such as increasing freedom of arrangement of the steering wheel and reducing weight of the vehicle.
In the above-mentioned steering apparatus, a torque sensor using a torsion bar is considered as its conventional detecting system of the steering torque, however, the system has problems that the torque sensor using the torsion bar is high in cost and that a freedom of design is limited because of size and placing position thereof are limited.
The present invention is made by solving the problems mentioned above, and an object of the present invention is to provide a linkless steering apparatus for a vehicle which does not require a torque sensor for detecting a steering torque which occupies a large space and is high in cost.
In accordance with a first aspect of the present invention, there is provided a steering apparatus, in which a steering mechanism for changing a direction (a steering angle) of a tire wheel is not mechanically connected to a steering wheel, a steering torque applied to the steering wheel is obtained and an actuator included in the steering mechanism is driven and controlled in accordance with the obtained steering torque, thereby increasing or decreasing steering angle, characterized by comprising: an electric motor connected to a rotational shaft of the steering wheel; a steering angle detector for detecting a steering angle of the steering wheel; and a calculator for calculating the steering torque based on the steering angle detected by the steering angle detector, a moment of inertia of the steering wheel, and a moment of inertia of the electric motor.
In this invention, the steering mechanism for changing a direction of the tire wheel is not mechanically connected to the steering wheel, the steering torque applied to the steering wheel is obtained, and the actuator included in the steering mechanism is driven and controlled in accordance with the obtained steering torque, whereby the steering angle is controlled so as to be increased or decreased. The electric motor is connected to the rotational shaft of the steering wheel and the steering angle detector detects the steering angle of the steering wheel. The calculator calculates the steering torque based on the steering angle detected by the steering angle detector, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor.
Therefore, it is possible to realize a linkless steering apparatus which does not need a torque sensor that occupies large space and is high-cost.
In accordance with a modification of the first aspect, there is provided a steering apparatus, further comprising a current detector for detecting an electric current flowing through the electric motor, wherein the calculator calculates the steering torque based on the electric current detected by the current detector, the steering angle of the steering wheel, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor.
In this invention, the current detector detects the current which flows through the electric motor. The calculator calculates the steering torque based on the electric current detected by the current detector, the steering angle detected by the steering angle detector, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor. That is, for example, even when the electric motor is operated as a reaction-force motor in the invention mentioned above, the calculator determines a reaction force which the electric motor actually generates based on the electric current detected by the current detector and calculates the steering angle by considering the reaction force.
Therefore, it is possible to realize a linkless steering apparatus which does not need a torque sensor that occupies large space and is high-cost, even in the case that the electric motor generates the reaction force.
More particularly, in the calculation of the steering torque in the former invention, the calculator calculates a steering angular acceleration based on the steering angle, adds the moment of inertia of the steering wheel and the moment of inertia of the electric motor, multiplies by the steering angular acceleration by the added result, and calculates the steering torque based on the multiplied result.
Further, in the calculation of the steering torque in the latter invention, the electric current flowing through the electric motor is detected by the current detector, and the calculator calculates the steering angular acceleration based on the steering angle, adds the moment of inertia of the steering wheel and the moment of inertia of the electric motor, multiplies the steering angular acceleration by the added result, further, adds the multiplied result and the value based on the electric current and calculates the steering torque based on the added result.
In accordance with a second aspect of the present invention, there is provided a steering apparatus, in which a steering mechanism for changing a direction (a steering angle) of a tire wheel is not mechanically connected to a steering wheel, a steering torque applied to the steering wheel is obtained and an actuator included in the steering mechanism is driven and controlled in accordance with the obtained steering torque, thereby increasing or decreasing a steering angle, characterized by comprising: an electric motor connected to a rotational shaft of the steering wheel; a rotational angle detector for detecting a rotational angle of the electric motor; and a calculator for calculating the steering torque based on the rotational angle detected by the rotational angle detector, a moment of inertia of the steering wheel, and a moment of inertia of the electric motor.
In this invention, the steering mechanism for changing a direction of the tire wheel is not mechanically connected to the steering wheel, the steering torque applied to the steering wheel is obtained, and the actuator included in the steering mechanism is driven and controlled, whereby the steering angle is controlled so as to be increased and decreased The electric motor is connected to the rotational shaft of the steering wheel and the rotational angle detector detects the rotational angle of the electric motor. The calculator calculates the steering torque based on the rotational angle detected by the rotational angle detector, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor. That is, with respect to the steering apparatus in accordance with the first aspect mentioned above, the detecting system for the steering angle is not required, and the rotational angle of the electric motor which has a relationship with the steering angle is detected and used in place of the steering angle.
Therefore, it is possible to realize a linkless steering apparatus which does not need a torque sensor that occupies large space and is high-cost.
In accordance with a modification of the second aspect, there is provided a steering apparatus, further comprising an current detector for detecting an electric current flowing through the electric motor, wherein the calculator calculates the steering torque based on the electric current detected by the current detector, the rotational angle of the electric motor, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor.
In this invention, the current detector detects the current which flows through the electric motor. The calculator calculates the steering torque based on the electric current detected by the current detector, the rotational angle detected by the rotational angle detector, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor. That is, for example, even when the electric motor is operated as a reaction-force motor in the invention mentioned above, the calculator determines a reaction force which the electric motor actually generates based on the electric current detected by the current detector and calculates the steering angle by considering the reaction force.
Therefore, it is possible to realize a linkless steering apparatus which does not need a torque sensor that occupies large space and is high-cost, even in the case that the electric motor generates the reaction force.
More particularly, in the calculation of the steering torque in the former invention, the calculator calculates a rotational angular acceleration based on the rotational angle of the electric motor, adds the moment of inertia of the steering wheel and the moment of inertia of the electric motor, multiplies the rotational angular acceleration by the added result, and calculates the steering torque based on the multiplied result
Further, in the calculation of the steering torque in the latter invention, the electric current flowing through the electric motor is detected by the current detector, and the calculator calculates the rotational angular acceleration based on the rotational angle of the electric motor, adds the moment of inertia of the steering wheel and the moment of inertia of the electric motor, multiplies the steering angular acceleration by the added result, further, adds the multiplied result and the value based on the electric current, and calculates the steering torque based on the added result.
In accordance with a third aspect of the present invention, there is provided a steering apparatus, in which a steering mechanism for changing a direction (a steering angle) of a tire wheel is not mechanically connected to a steering wheel, a steering torque applied to the steering wheel is obtained and an actuator included in the steering mechanism is driven and controlled in accordance with the obtained steering torque, thereby increasing or decreasing a steering angle, characterized by comprising: an electric motor connected to a rotational shaft of the steering wheel; a counter voltage detector for detecting a counter voltage of the electric motor; and a calculator for calculating the steering torque based on the counter voltage detected by the counter voltage detector, a moment of inertia of the steering wheel, and a moment of inertia of the electric motor.
In this invention, the steering mechanism for changing a direction of the tire wheel is not mechanically connected to the steering wheel, the steering torque applied to the steering wheel is obtained, and the actuator included in the steering mechanism is driven and controlled, whereby the steering angle is controlled so as to be increased and decreased. The electric motor is connected to the rotational shaft of the steering wheel and the counter voltage detector detects the counter voltage of the electric motor. The calculator calculates the steering torque based on the counter voltage detected by the counter voltage detector, the moment of inertia of the steering wheel, and the moment of inertia of the electric motor. That is, with respect to the steering apparatus in accordance with the first and second aspects mentioned above, the detecting systems for the steering angle and the rotational angle of the electric motor are not required, and the counter voltage of the electric motor which has a relationship with the steering angle and the rotational angle is detected and used in place of the steering angle.
Therefore, it is possible to realize a linkless steering apparatus which does not need a torque sensor that occupies large space and is high-cost.
More particularly, in the calculation of the steering torque in the present invention, the calculator adds the moment of inertia of the steering wheel and the moment of inertia of the electric motor, multiplies the counter voltage by the added result, and calculates the steering torque based on the multiplied result.
Further, as is described later, in the case of actively using the electric motor as a reaction-force motor which applies a force (a reaction force) in a direction opposite to the operating direction of the steering wheel, it is actually impossible to detect the counter voltage. However, in the case of passively using the electric motor as a detecting system for the counter voltage not as the reaction force motor, the above definition is not employed.
Further, in accordance with the other modification.of the present invention, there is provided a steering apparatus as recited in the first and second aspect mentioned above, wherein the electric motor is a reaction-force motor which applies a force to the steering wheel in a direction opposite to an operating direction of the steering wheel.
In this invention, the electric motor connected to the rotational shaft of the steering wheel is the reaction-force motor which applies the force (the reaction force) to the steering wheel in the direction.opposite to the operating direction of the steering wheel.
Therefore, it is possible to employs the existing reaction-force motor as for the purpose of giving the same steering feeling as that of the linked steering apparatus to the driver in the linkless steering apparatus, as the electric motor In this case, as mentioned above, in the steering apparatus in accordance with the third aspect, the electric motor can not be replaced by the reaction-force motor, however, another electric motor can be further provided in addition to the reaction-force motor.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.